Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$72.63	8.130%	$78.5348	$78.53	$78.55	$78.50
Purchase #2	$75.91	9.121%	$82.8338	$82.83	$82.85	$82.80
Purchase #3	$226.57	3.132%	$233.6662	$233.67	$233.65	$233.70
Purchase #4	$91.25	11.588%	$101.8241	$101.82	$101.80	$101.80
Purchase #5	$146.38	7.221%	$156.9501	$156.95	$156.95	$157.00
Purchase #6	$173.74	3.368%	$179.5916	$179.59	$179.60	$179.60
Purchase #7	$70.69	11.580%	$78.8759	$78.88	$78.90	$78.90
7 purchase totals =	$857.17		$912.2765	$912.27	$912.30	$912.30